Balloon catheters for IABP are often used in medical treatment of heart diseases. In the treatment, a balloon catheter is inserted into the artery near the heart of the patient, and the balloon is inflated and deflated in accordance with the heart beat of the patient in order to assist or activate the cardiac function. Japanese Patent Application Laid-open No. 60-106464 (hereinafter "JP '464") discloses a medical-purpose driving apparatus for inflating and deflating such balloons.
The driving apparatus disclosed in JP '464 has a primary tube line and a secondary tube line, which are separated from each other by a pressure-transfer isolator (simply called an isolator, or generally named a volume limiting device (VLD)). A change of pressure occurring in the primary tube line is transferred to the secondary tube line, and the resultant pressure change occurring in the secondary tube line inflates and deflates the balloon. The reason why the primary and secondary tube lines are separated is that different kinds of fluid gas are used in these two lines, namely, one as a driving medium for actually driving the balloon, the other as a pressure source for generating positive pressure and negative pressure. This is required to improve the response of inflation/deflation of the balloon and, at the same time, to generate necessary pressure at low cost. The pressure-transfer isolator is located between the pressure source and the balloon in order to prevent excessive gas from flowing into the balloon when the balloon is inflated.
In this Intra Aortic balloon catheter, helium gas, which has a small mass and a high response ability, is preferably used as the fluid gas filled in the secondary tube line. In this case, the helium gas functions as driving shuttle gas. Prior to filling the balloon and the secondary tube line with the helium gas, the balloon and the secondary tube line are evacuated. The pressure of helium gas to be filled is up to pressure near the atmospheric pressure or lower than that pressure. Filling pressure up to 10 mm Hg higher than the atmospheric pressure is acceptable, so that the deflation speed of the balloon can be increased, and the response to high heart rate is improved. It can also reduce the load on the heart muscle.
In the conventional technique, the primary tube line consists of a positive pressure line and a negative pressure line, and the positive and negative pressures are alternately transferred to the pressure-transfer isolator by means of a valve. The positive pressure line has a positive-pressure generating pump and a positive pressure tank, while the negative pressure line has a negative-pressure generating pump and a negative pressure tank. In other words, in the conventional method, positive pressure and negative pressure are generated by separate pressure sources.
Another type of driving apparatus for medical appliances is disclosed in Japanese Patent Application Laid-open No. 60-116366 (hereinafter "JP '366"). The driving apparatus of JP '366 uses a compressor as a positive-pressure generator, and a vacuum pump as a negative-pressure generator. The output ports of the respective pressure generators are connected to open/close valves. The output ports of the valves are connected to, for example, an artificial heart, which is driven by positive and negative pressure supplied through the valves.
However, providing two separate pressure generators is undesirable from the viewpoints of electric power consumption and the weight of the apparatus. In order to overcome this drawback, Japanese Patent Publication (after examination) No. 3-28595 (hereinafter "JP '595") and Japanese Patent Publication No. 4-61661 (hereinafter "JP '661") propose to use a single pressure generator having an input port, at which negative pressure is generated, and an output port, at which positive pressure is generated. The single pressure generator is used to generate positive and negative pressure to drive the balloon catheter.
The total weights of the driving apparatuses disclosed in both JP '595 and JP '661 are reduced, however, have problems in energy efficiency.
In JP '595, when the pressure of the positive pressure tank exceeds a predetermined level, the excessive pressure is released in the atmosphere using an solenoid valve connected to the output port of the pressure generator. This structure requires a check valve between the positive pressure tank and the solenoid valve in order to prevent too much pressure from being released. Similarly, when the negative pressure is reduced below a predetermined value, the input port of the pressure generator is opened to the atmosphere through another solenoid valve, and another check valve is required between the negative pressure tank and the input port. The energy efficiency of the apparatus apparently becomes worse when the pump (i.e., the pressure generator) is driven under condition beyond the predetermined pressure, because the input and output ports of the pump are opened to the atmosphere to regulate the pressures to the desired levels. During the period that the input or output ports opens, the pump is generating a useless pressure that does not contribute to driving the balloon. If a pump having a comparative low output is used in order to shorten the period of time that the input or output ports open, the pump cannot supply sufficient positive pressure when the heart beat rate of the patient has increased. To avoid such a situation, it is necessary to use a pump having an excessive power and to discard a portion of its output.
In JP '661, the driving apparatus has a switching valve between the positive side of the pressure generator and the positive pressure tank. This valve is open to connect the positive pressure tank and the positive side of the pressure generator until the pressure of the positive pressure tank reaches a predetermined value. When the pressure of the positive pressure tank has exceeded the predetermined value, the valve shuts off the connection and, at the same time, opens the positive side to the atmosphere.
Another switching valve is provided between the negative side of the pressure generator and the negative pressure tank. The negative side of the pressure generator is connected to the negative pressure tank via this valve until the negative pressure of the tank reaches a predetermined value. When the pressure of the negative pressure tank has lowered below the predetermined value, the valve shuts off the connection and opens the positive side to the atmosphere.
Similar to JP '595, the energy efficiency worsens when one or both of the ports are opened to the atmosphere. In either JP '595 or JP '661, the energy efficiency of the driving apparatus is likely to easily drop if the object to be driven is small, or if the heart beat rate is low (or if the inflation/deflation cycle is long).
In other words, in accordance with the conventional apparatuses, the energy efficiency becomes worse, especially when only a small amount of work is required. Low energy efficiency causes a high power consumption, so that the power source capacity must be kept large even though the number of pumps is reduced.
Since the medical-appliance driving apparatus is carried to many places inside and outside of the hospital, it is desirable for the built-in power source capacity to be made as small as possible. However, the conventional apparatuses require high power of the built-in power source because of high power consumption.
Japanese Patent Application Laid-Open No. 5-261148 (hereinafter "JP '148") also discloses a driving apparatus that has a similar drawback. A portion of the output from the pressure generator is abandoned, and the energy efficiency of this apparatus is not good enough.
Actually, it is a great advantage for a driving apparatus, especially those used for an artificial heart or an intra-aorta balloon, to reduce the number of pumps (i.e., pressure generators) from two to one because the weight and the number of components can be reduced.
However, in the conventional driving apparatuses, the positive and negative pressure applied to the output ports must be kept within a certain range. For this reason, a larger sized pump is used in accordance with high heart beat rate, while a portion of the generated pressure is abandoned in the normal condition. Thus, the low energy efficiency of the conventional apparatus can not be avoided.
In the conventional medical-appliance driving apparatuses, the secondary tube line and the balloon must be evacuated before they are filled with shuttle gas (e.g., helium gas). This requires an additional evacuation pump and, accordingly, causes the conventional driving apparatuses for medical appliances to become large and heavy with a number of components.
By the way, IABP driving apparatuses or AH (artificial heart) driving apparatuses generally have an alarm system, for detecting a malfunction or a defect of the balloon membrane, or other devices under various circumstances. However, for example, in order to find a very small pin hole in the balloon membrane, which may cause frequent supply of helium gas, not only the operation information at the alarm point of time, but also several tens of hours of past data, including the information about the normal operation and the information immediately before the alarm, are required. Whenever an alarm occurs, some of the conventional driving apparatuses (e.g., KAAT manufactured by Kontron Inc.) output, the blood pressure and the electrocardiograph of the patient, the balloon activation waveform, and the reason for the alarm on the printed papers by printer. This type of driving apparatus also outputs these data on the printed papers when the patient's condition changes for the worse with, for example, a disorder in the electrocardiograph, even if the system itself is normally working. It is confusing to have to distinguish between the malfunction of the system and the change of the patient's condition. In addition, a great volume of paper is consumed wastefully.
Of course, it has been proposed to connect the medical-appliance driving apparatus to a personal computer via a parallel interface and transmit the data, including the operational state of the system, to the personal computer.
However, the power source of a general-use personal computer does not have a sufficient insulating ability, and it is likely to cause leakage current to increase in the patient's body if such a general-use personal computer is connected directly to the driving apparatus having an electrocardiograph input unit. Accordingly, it becomes necessary to insulate the interface to the personal computer using an optocoupler or an optoisolator. Because multi-channel parallel interfaces are not preferable with respect to cost and operation, an attempt is being made to connect the medical-appliance driving apparatus to the personal computer using a serial interface.
Unfortunately, it takes several tens of minutes for the serial interface to transfer the past data stored in the memory of the driving apparatus to the personal computer, depending on the amount of data stored. In practice, if a problem is detected in the apparatus, the stored data, such as the past and current operation data, must be transferred to the computer as soon as possible for analysis of the problem because any adverse influence to the patient must be avoided. Although a parallel interface can improve the data transmit speed, it must be insulated from the personal computer, which requires additional cost and components.